1. Field of the Invention
The field of the invention relates to medical imaging generally, and more particularly, to radioscopy.
2. Description of Prior Art
Radioscopy is nowadays widely used for diagnostic and therapeutic operations carried out under imaging control. Radioscopy is a functional imaging method that consists in observing the image of internal organs produced on an X-ray detector by interposing the body between said detector and a beam of X-rays. Radioscopy brings into relation imaging, the guiding instrumentation equipment and the practitioner.
Interventional radioscopy typically involves the introduction of guiding instrumentation equipment such as a catheter equipped with a specific device into the vascular bed of the patient to carry out an intervention, in association with an injection of contrasting agent to make the vessels temporary visible. The progression of the manipulation of the equipment is viewed and is controlled by means of X-rays.
Compared to surgery, this interventional approach can be carried out without making any major cut or incision and leads to a much shorter recovery time and stay in hospital.
However, this type of radioscopy device has disadvantages. Indeed, the radioscopic images are viewed in real time with an intensity of the beam of X-rays spread out over a long time. For an average examination, the total quantity of X-rays emitted during the exposure is high, which can thereby cause a too high irradiation. Such irradiations lead in the short and the long term to health problems both for the patient and for the medical personnel. To aid the resolution of this problem of irradiation, there exists in the background art a conventional solution consisting in reducing the intensity of the beam of X-rays by around 100 times compared to the intensity of the beam of X-rays in a standard radiographic examination.
The immediate consequence of the use of a relatively low intensity is a reduction in the quality of the image compared to radiography. This reduction in quality manifests itself in a significant deterioration in the signal to noise ratio of the content of the images, observable through the scintillation and the granularity of the image, which commonly results in a noisy image.
Moreover, the reduction in the intensity of the beam of X-rays deteriorates the visibility of the guiding instrumentation equipment. The time spent carrying out the intervention is increased by the difficulty that the physician encounters in correctly viewing his guiding equipment. In the case of a guide constituted of a metal wire of low thickness, the radio opacity is low. Consequently, the guiding equipment has a very low contrast to noise ratio in the image. This contrast to noise ratio is typically between 1 and 4 in fluoroscopy and can sometimes drop below 1. The detection of pixels belonging to the guiding equipment is thereby difficult to implement due to the fact of their very low contrast to noise ratio in the image.
At present, steerable filtering methods exist that enable linear structures in an image to be detected or highlighted.
Examples of this type of steerable filtering are described in the following documents:
“The design and use of steerable filters,” Freeman and Adelson, IEEE trans. Patt. Anal. And Machine Intell., Vol. 13, No. 9, pp. 891-906, September 1991.
Danielsson, P.-E. and Q. Ye (1988). “A new procedure for line enhancement applied to fingerprints,” In E. S. Gelsema and L. N. Kanal (Eds.), Pattern Recognition and Artificial Intelligence, the Third Pattern Recognition in Practice workshop, Amsterdam, pp. 49-61.
“Recursive Gaussian Derivative Filters,” Proceedings of the 14th International Conference on Pattern Recognition, ICPR'98, Brisbane (Australia), 16-20 Aug. 1998, IEEE Computer Society Press, Vol. I, pp. 509-514.
“Fast anisotropic gaussian filtering,” IEEE TRANSACTIONS ON IMAGE PROCESSING, VOL. 12, NO. 8, August 2003.
However the filterings described in the above documents have disadvantages. Indeed, these filters are not suited to the detection in a radioscopic image of an object as longilinear as a guiding equipment and having such a low contrast to noise ratio.